Our long-term goal is to understand olfactory coding in the central nervous system. In this proposal, we will investigate stereotyped odor representation in Drosophila mushroom body and test the hypothesis that spatial patterns of activity examined encode odor information. The organization and functional logic of early olfactory system appears remarkably similar in Drosophila and mammals. An outstanding feature of this system is the topographic map of receptor activity segregated in glomeruli. Yet, how such spatial patterns of activity are transformed to higher centers and then translated into odor perception remains illusive. Taking advantage of a relatively simple nervous system and our newly developed imaging method, we have been able to reveal odor-evoked stereotyped activity patterns in one of the higher centers, mushroom body. In this proposal, odor-induced neuronal activity in the regions of cell bodies and dendrites of mushroom body will be monitored via Ca 2+ imaging from living flies. In this preparation, a global view of spatial patterns of activity is obtained by conventional microscope while activity in individual neurons is analyzed by 2-photon laser microscope. We will investigate the basic properties of this stereotyped odor representation, including how single odorants, mixed odorants, and concentrations of odorants are represented in spatial patterns of activity. Then, we will examine physiological significance of spatial patterns of activity in odor discrimination by comparing results of imaging analysis with behavioral tests. Finally, we will use genetic manipulation to help to dissect how odor information is organized in spatial patterns of activity in mushroom body.